1. Field of the Invention
The present invention relates generally to a reflective display device, such as electronic paper, and, more particularly, to a reflective display device having divided electrodes, which reduces the asymmetry of drive voltages by modifying the shape of scan electrode pattern.
2. Description of the Related Art
Electronic paper, which is a kind of reflective display device, is a new display device having the advantages of an existing display device as well as printed paper, and is one of representative next generation display devices currently being developed, along with a Liquid Crystal Display (LCD), a Plasma Display Panel (PDP) and an organic ElectroLuminescent (EL) device.
Such electronic paper is classified as Gyricon-type electronic paper using twist balls, electrophoresis-type electronic paper using electrophoresis and microcapsules, cholesterol liquid crystal-type electronic paper using cholesterol liquid crystals, and collision electrification-type electronic paper using such as toner particles.
Among the various types of electronic paper, the collision electrification-type electronic paper is a display device having a thickness of about 0.1 mm, in which white and black particles fill a gap between transparent films, and which uses the phenomenon in which, due to collisions that occur when toner particles are coated with silica to which an electrification promoter is added and an electric field is applied thereto, the toner particles are charged, the polarity of the charge is determined by the electrification promoter.
FIG. 1 is a sectional view showing the internal structure of the principal portion of a typical collision electrification-type electronic paper display device, and FIG. 2 is a plan view showing the electrode arrangement structure of the typical collision electrification-type electronic paper display device.
The typical collision electrification-type electronic paper display device is described with reference to FIGS. 1 to 3 below. Referring to FIG. 1, two types of particles 32 and 34, having different colors, are distributed in each of a plurality of cells, which are formed by dividing a space between two substrates 10 and 20 using the barrier ribs 30. In this case, when a voltage is applied across the electrodes 12 and 22, which are respectively patterned on the two substrates 10 and 20, positively charged particles move to a (−) electrode, and negatively charged particles move to a (+) electrode.
In the above-described electronic paper display device, each of the pixels is generally formed in a square shape. Particularly, in the case of a color display device, a single pixel is divided into three sub-pixels so as to implement Red (R), Green (G) and Blue (B) colors.
Referring to FIG. 2, a single scan electrode 12 extends through a single pixel cavity, and three data electrodes 22, which cross the single scan electrode 12, extend corresponding to respective sub-pixels. Accordingly, the single scan electrode 12 is formed to have a width three times as great as that of each of the three data electrodes 22.
The above-described different electrode width between the scan electrode 12 and the data electrodes 22 makes electric field distribution non-uniform between the two substrates 10 and 20, and therefore, as shown in FIG. 3, the data electrodes 22 having a relatively small width causes denser electric field distribution than the scan electrode 12.
For reference, although FIG. 3 shows a view obtained by rotating one of the two electrode groups by 90 degrees in a direction parallel to a corresponding substrate to facilitate the comparison of the widths of the two electrode groups, the two electrode groups are actually disposed to cross each other.
As described above, the data electrodes 22 are implemented to have a width smaller than that of the scan electrode 12 and, thus, a dense electric field distribution is exhibited, so that, when the display device is driven, a drive voltage for changing a black color into a white color and another driving voltage for changing a white color into a black color differ from each other, in which asymmetry of the drive voltages results.
Therefore, problems occur in that, when drive waveforms are designed and drive Integrated Circuits (ICs) are manufactured, a voltage supply source and a drive circuit are additionally required due to the asymmetry, therefore the above-described asymmetry of the drive voltages causes a number of difficulties related to conducting drive control as well to the design of circuitry.